Generally, a wireless communication system, which is configured by including a Base Station (BS) and a User Equipment (UE) extensively (or broadly) provides diverse types of communication services including audio or video, and so on, to user devices through one base station or more than one base station, and, generally, one base station may provide one or more cells.
The structure of a recent wireless communication system is changing from a macro cell based centralized base station format, which corresponds to a related art vertical hierarchy, to a base station format, wherein diverse forms of small cells, such as pico cell, femto cell, and so on, are inter-connected to a macro cell.
Meanwhile, recently, in accordance with the gradual increase in efforts for reducing greenhouse effect, which is caused by excessive discharge of carbon dioxide, and environmental destruction, the power of base stations is being considered as the factor discharging the largest amount of carbon dioxide even in the field of mobile communication, and how much the power of base stations can be reduced or how efficiently the power of the base station is to be used has become an important issue.
Up to recently, in order to increase the mobility of the user equipment, more focus is maintained on efficiently using the power of the user equipment and reducing energy consumption. However, from now on, by efficiently using the power of the user equipment, not only can the discharge of carbon dioxide be reduced by decreasing the consumption of energy, but Operation Expenditure (OPEX) may also be saved.
Therefore, the need for technology development for reducing power consumption of base stations through efficient energy consumption of base stations is growing, and, in 3GPP (3rd Generation Partnership Project), discussions of an energy saving solution in the view point of base stations have started since Release 9, and, currently, in Release 12, discussions are being made on the technologies for energy saving between LTE (Long Term Evolution) base stations during off-peak time.
For energy saving of the base station, it may be considered to shift the base station to a Power Off or Idle state. In this case, the base station that is shifted to the Power Off or Idle state may perform handover on User Equipments existing in its Coverage area to neighboring base stations, which are capable of compensating for the coverage of the corresponding base station.
However, even though part of the coverage areas may overlap between the base station and the neighboring base station, each of the base stations does not fully cover the other's coverage area, since there are no separate signaling procedures between the base station and the neighboring base station, in case the base station shifts to the Power Off or Idle state, a situation where the base station cannot properly compensate for the coverage of the base station may occur, thereby causing the handover to fail. Furthermore, even if the handover is realized, in the standing point of the neighboring base station, the user equipments may correspond to user equipments existing in the coverage boundary, which may lead to a problem of significant degradation in the Quality of Service being provided to the user equipments.
Accordingly, the introduction of a method of allowing the neighboring base station to compensate for all of the coverage of the base station without any lacking parts and a method of allowing the quality of services being provided to the user equipments to be maintained during the handover is required, and a solution (or scheme) for resolving this is required.